190 THE CHINESE
An Lu-shan's defection and the accompanying disorder un-
leashed other forces. From the northern and western frontiers
came raiding barbarians, ever ready to pounce on the fertile and
wealthy plains and valleys to the south. The Tibetans especially
were persistent, and at one time took Ch'angan (763). In stem-
ming invasions and reducing internal revolts the T'ang summoned
non-Chinese peoples to their assistance. It will be recalled that
the founder of the dynasty, Li Yuan, had a Turkish mother, and
:he vigor of his line may be attributed in part to non-Chinese
blood. While the most competent of the imperial generals of the
period, Kuo Tzii-i, who more than any other was responsible for
the defense and perpetuation of the T'ang, was a Chinese, he was
from Shansi and may possibly have had non-Chinese blood in his
veins. The next greatest of the T'ang commanders of the time, Li
Kuang-pi, was of Khitan stock. Even these were unable to defeat
the Tibetans and reduce the rebellions with purely Chinese forces
but called to their assistance the Uighurs, had Moslem Arabs in
their armies, and brought in foreign troops even from Ferghana.
It will be remembered, too, that the farthest extension of the T'ang
power westward was under the direction of a general of Korean
extraction. All this was quite different from the Han, when the
commanders and the conquering armies appear to have been en-
tirely or chiefly Chinese. Even with the support of aliens, the
military achievements of the T'ang in its heyday were probably
no more remarkable than those of the Han—although the T'ang
Empire occupied a somewhat wider area—and in some respects
were not so noteworthy.
Did this mean a decline in the vigor of the Chinese race? We
do not know. The Chinese were certainly to increase in numbers
and to occupy, as farmers and merchants, more territory, but it
may be significant that during somewhat more than half the time
that has elapsed from then to now at least part of the territory
inhabited by the Chinese has been under foreign control, that
during a third or a fourth of it all the Chinese have been subject
to foreigners, and that never since the T'ang—except for the brief
years of the Republic, when the Empire was maintained (and
even that only partially) under the momentum acquired under
the Manchus—has China under purely native rule attained to the
total area in square miles that it reached under the T'ang. It i?